A modified TOP assay to detect per- and polyfluoroalkyl substances in aqueous film-forming foams (AFFF) and soil

Md Al Amin; Yunlong Luo; Feng Shi; Linbo Yu; Yanju Liu; Annette Nolan; Olalekan Simon Awoyemi; Mallavarapu Megharaj; Ravi Naidu; Cheng Fang

doi:10.3389/fchem.2023.1141182

A modified TOP assay to detect per- and polyfluoroalkyl substances in aqueous film-forming foams (AFFF) and soil

Front Chem. 2023 Oct 10:11:1141182. doi: 10.3389/fchem.2023.1141182. eCollection 2023.

Authors

Md Al Amin^{1

2}, Yunlong Luo^{1

2}, Feng Shi^{1

2}, Linbo Yu^{1

2}, Yanju Liu^{1

2}, Annette Nolan³, Olalekan Simon Awoyemi¹, Mallavarapu Megharaj^{1

2}, Ravi Naidu^{1

2}, Cheng Fang^{1

2}

Affiliations

¹ Global Centre for Environmental Remediation (GCER), University of Newcastle, Callaghan, NSW, Australia.
² CRC for Contamination Assessment and Remediation of the Environment (CRC CARE), University of Newcastle, Callaghan, NSW, Australia.
³ Ramboll Australia, The Junction, NSW, Australia.

Abstract

Total oxidisable precursor (TOP) assay can oxidise some per- and polyfluoroalkyl substances (PFASs) and their precursors, most of which cannot be quantitatively detected so far, and convert them to detectable PFASs, such as perfluoroalkyl acids (PFAAs). However, the conversion is constrained by the complexity of the target samples, including co-existent organics, unknown PFAS precursors, and background. In this study, the TOP assay is modified to increase the oxidation and conversion efficiency by changing the initial concentration of target sample, increasing oxidising doses, time, temperature, etc. The modified TOP assay is applied to test several aqueous film-forming foams (AFFF) and a PFAS-contaminated soil extract. The sum concentrations of the detectable PFASs are increased by up to ∼534× in the AFFF samples and ∼7× in the PFAS-contaminated soil extract. The detectable fluorotelomer sulfonate (FTS, such as 6:2/8:2 FTS) is accounted as an oxidation indicator to monitor the oxidation and conversion progress of the oxidisable PFASs precursors to the detectable PFASs. Overall, the modified TOP assay could be an appropriate method for identifying missing PFASs mass in complex matrices by detecting the PFASs precursors effectively.

Keywords: AFFF; PFAS precursors; TOP assay; fluorotelomer sulfonate (FTS); oxidation efficiency; solid-phase extraction (SPE).

Grants and funding

The authors kindly acknowledge the funding supported by ARC (SR180200015) and the postgraduate research scholarship (UNIPRS and UNRSC) (50:50) provided by The University of Newcastle. The authors also appreciate the funding support from Cooperative Research Centre for Contamination Assessment and Remediation of the Environment (CRC CARE).